Can Glue Mold? How and Why Does This Happen?

I’ve been on a cleaning kick lately. Not in a Marie-Kondo-this-doesn’t-spark-joy kind of way, but in a I-haven’t-cleaned-out-my-basement in-about-10-years-so-I-should-probably-do-that kind of way.

Yeah.

During said cleaning, I located a lot of stuff I can repurpose for dollhouse building. Cardboard, decorative items (ribbons, sticky gems), and glue. Lots and lots of glue. Mostly it’s glue sticks and white glue, but I’ll find ways to use it.

Except for this bottle.

This is… I don’t even know

What was once white glue is now brownish yellowish glue. I promise it’s not wood glue or any other kind of glue. Here’s a side by side.

Old glue

Not old glue

This brown glue is old white glue.

As I examined the bottle more closely, I found a bunch of black specks in one corner.

Um, what?

Um. OK. What the heck is that? Is it mold? Can glue mold? How? And why?

How Long Does Glue Last?

I never thought about the fact that glue might have an expiration date. I mean, I always knew that if I didn’t close the cap tightly, it would dry out. But, that’s not the same as going bad or, worse, mold.

Wet supplies, like glue or paint, only last one to two years. That’s because once you’ve opened the product you’ve exposed it to oxygen. I don’t want to make this into a big old science lesson but, as I’m sure you know, exposing wet stuff to oxygen generally dries it out (humid summer days notwithstanding).

Once you open your paint, glue, paste, whatever, it’s best to use it up ASAP, because now you’ve exposed your supply to oxygen and the clock is ticking. Between uses, seal it up nice and tight. If you’re having problems resealing the original container, cover it with an airtight layer of plastic wrap, then maybe pop it in a zip-top bag. Just make sure you squeeze the air out before you seal the bag.

But there’s a huge sale!

I get it. Craft supplies are expensive. And, when there’s a fantastic sale, you want to buy up all the supplies you could ever need. You figure you’ll use it all up eventually, anyway, so stock up and save!

Until you get to that last of your stash and, well, it’s just not right. The paint color is off, and the glue isn’t quite as sticky. But, you think, this has been sealed this whole time. It should still be fine, right?

Well, let me ask you. When was it made?

What now, you say? I don’t know. I bought it a few years ago during that super awesome sale.

OK. But, when was it made. Because, if you know when it was made, you’ll have a better idea of when it expires.

Glue has an expiration date?

Yup.

I know, I was shocked, too. But, it’s right there on the bottle. Problem is, it’s not exactly in plain English.

Interpreting the tea leaves

Refer back to the glue pictures. Specifically, the one with the “good” glue. Look at the top of the bottle. You see all of those numbers and letters? That’s where the expiration date is hidden!

I know. It’s gibberish, or glue speak, I suppose. But, once you’ve deciphered the code, you’ll know when a bottle of glue was manufactured, which goes a long way toward helping you know how long you really have to use up that glue.

Keep in mind, that’s not the same as an expiration date. If you ask around, most glue manufactures will tell you that their product has a shelf life of about two years. Good to know. But, just because you bought something two years ago, doesn’t mean it’s got two years life left in it. It might have less.

Given that glue is not milk, using expired glue won’t make you sick. It might annoy you because it’s not as sticky, but it’s fine to use. And, remember that the manufacturing date doesn’t mean as much if you’ve already opened the bottle and started using it. Once you’ve cracked the seal, you should use the glue as quickly as you can.

Glue speak

And, while the information I’m about to give you is specific to my brand of white glue (Elmer’s white glue, to be exact), from what I’ve found, most glue codes are pretty similar to Elmer’s. You may, however, have to do a little digging to find the right code ring for your specific brand.

Look back at the picture of the good glue again. The code on my bottle is Y25HD61 P2.

Super helpful.

Everyone said that the Elmer’s glue code starts with a letter, and that letter corresponds to the year of manufacture. One source said “H” stands for 2005, then “I” is 2006. However, another source said “H” is 2002, and “I” is 2003.

As you can see, my code starts with a Y, and I have no idea what Y correlates to. If I start with H as 2002, then my bottle was manufactured in 2019. If I use H as 2005, then my bottle was manufactured in 2022.

I promise you, neither of these scenarios is possible.

Sigh.

What I can tell you is that based on the Internet decoding rings, this bottle of glue was created on the 25th day of August. I know this because the two-digit number after the Y is 25, which is the date of the month the bottle was manufactured. The next letter after that two-digit number is H, which correlates with August. How? A is equal to January, B is February, and so on, until you get to H, the 8th letter, which is the eighth month of the year: August.

I tried the same trick with the old bottle, but the code is rubbed off, that’s how old it is.

So, I guess the lesson here is to not lose bottles of glue and use them up before they mold.

How Does Glue Mold and More Importantly, Why Does Glue Mold?

I’ll never know how old those glue bottles are. Oh, well. But now, my curiosity is alive and well. Why did the old bottle grow mold? I mean, I know exposure to air causes things to degrade and break down, but glue is synthetic, right?

There’s the old joke about horses going to the glue factory, (which is actually based in reality). But, this is white glue I probably paid two bucks for. There’s no way there’s organic material that would decompose in there, right?

What is glue made of?

While I’ve talked about the different types of glue before, I’ve never talked about what glue is made of.

Sticky stuff. You’re welcome.

All kidding aside, the “sticky stuff” used to be, well, animal collagen. That’s why the joke about going to the glue factory persists. I’ll gloss over the details, but muscles, bones, and tissues contain collagen. I’m sure you’ve heard of it. Even humans have it (and lose it as we age). Collagen is sticky when it’s wet, but when it dries, it turns into a hard substance that’s not water-soluble. Read: it keeps things stuck together.

While you can get animal-based glues these days, they aren’t in widespread use in the general crafting world or schools. Most general-purpose glues these days are synthetic. Synthetic glues are a mix of polyvinyl acetate (PVA), ethanol, acetone, and other stuff. There’s also water in it to help create the thin, easy to squeeze out of the bottle consistency. Also, water helps the glue dry evenly.

For the record, there is no ingredients list on either bottle of my glue. I checked the Elmer’s website but because the specific ingredients are “proprietary information,” they aren’t sharing. That’s cool. They do, however, say that their products are “chemical based” and that said chemicals are “synthesized (created by Man).”

Can Glue Mold If It’s Synthetic?

Since I’m dealing with synthetic glue, I wondered how in the world synthetic chemicals grow mold. Mold is a fungus that decomposes (as in, eats) organic material: leaves, plants, wood, your forgotten leftovers.

None of the ingredients in synthetic glue meet this definition.

However, in addition to “food,” mold needs one other thing to grow.

Water.

Ah. That’s my answer — sort of.

Mold needs water and oxygen to grow. It also needs the right temperature. And, that’s between 40 and 100 degrees Fahrenheit. You know, like your house.

I used a bunch of the glue (as you can see), then forgot about it (which sounds like me). While I’m sure I closed the bottle correctly, there’s still that gap in the bottle. That’s the air the mold needs. Mix that with the water in the glue, plus the right temperature, and you get mold.

Gross.

Also, science!

How Do I Stop My Glue from Molding?

You don’t. I’m pretty sure, though I’m not an expert, that mold is just a fact of life. And, the thing with glue is that you can’t do anything about the water. It’s there. The end. With that water and inevitable exposure to air, mold will eventually grow.

The best way to prevent mold growth is to use up all the glue as fast as you can once you open a bottle. Once you’ve cracked that seal, time is ticking.

You could labeling and tracking the buy date and open date on all of your craft supplies. Then, manufacturing date aside, you’ll have a good idea of when you need to use it all up.

Also, if you are doing this, please share your secrets on keeping up with this!

Learn from My Glue Mistakes

It’s a sticky situation (don’t judge me!) but one worth noting. I tend to buy in bulk when things are on sale, then promptly forget about them. Ask my basement.

But, now that I know these things have shelf lives, I’m going to use up what I’ve got until I absolutely need more. With 20 glue sticks (I am not kidding), I’m probably going to see more mold before I use them all.

Have you ever found moldy craft supplies? Any tips to extend supply shelf life?